Increases in fuel prices as well as well as in exhaust gas regulations has resulted in an increase in the popularity of alternative propulsion systems for vehicles. Hybrid propulsion systems may utilize a propulsion combination of battery and internal combustion engine. A common operating mode for a battery/internal combustion engine hybrid propulsion system is for the engine to shut off when the vehicle comes to a stop (a traffic stop light, for instance) and then to launch and initially drive the vehicle on battery power until the internal combustion engine is again required to supplant the battery. Such a powertrain system is referred to as a start/stop hybrid propulsion system. One challenge for vehicle designers with such a hybrid propulsion system is the maintenance of appropriate temperatures in the engine, the transmission, the exhaust system and in the passenger compartment during cold ambient temperatures when frequent engine deactivation is occurring (ex. start/stop city driving). One proposed solution to the temperature challenge provided by start/stop hybrid propulsion systems is to utilize a heat recovery system, in association with the engine exhaust system to reclaim waste heat. For example, the engine coolant, or other thermal transfer medium, may be passed through a heat exchanger associated with the engine exhaust system to capture waste heat and supplement the vehicle needs for heat during periods in which the engine is off.
With increasingly stringent emission regulation, exhaust gas after treatment systems have become increasingly complex in size, number of components and cost. Existing after treatment systems typically utilize individual components that each has a discreet function. The components often must be arranged in a particular configuration, and with a particular spacing or separation, at times dictated by the vehicle architecture. The sizes of the individual components and the packaging within vehicle architectures vary, but it is clear that the size and spacing of the components may impose a significant thermal load which operates to rapidly reduce the temperature of exhaust gas passing therethrough and, the waste heat which may be recovered therefrom.
A typical exhaust after treatment system for a gasoline fueled internal combustion engine involves the placement of a catalyst treatment device in close proximity to the exhaust manifold of the internal combustion engine. This catalyst treatment device, referred to as a close-coupled converter, is typically the catalytic device in which most regulated exhaust constituents are converted (>90%). The close coupling to the engine minimizes thermal loss in the exhaust gas, between the engine and the device, resulting in higher temperatures and quicker catalytic activation since the catalyst compounds that are typically used for treating engine exhaust gas operate best at temperatures in excess of 350° C. A second catalyst treatment device, often referred to as an under floor converter is typically placed some distance from the close coupled converter and, as the name implies, often under the floor of the vehicle, behind the engine. In the case of an internal combustion engine having front-exiting exhaust ports, the distance between the close coupled converter and the under floor converter can be 1 meter or more. Such a distance will result in substantial heat loss from the exhaust gas prior to its entry into the second, under floor converter. Such undesirable heat loss operates to reduce the effectiveness of the under floor converter and, substantially reduces the heat available downstream of the under floor converter for recapture by a heat exchanger which, by necessity must be placed downstream of both catalyst treatment devices so as to maximize available exhaust gas heat for their operation.